1. Field of the Invention
The present invention generally relates to a flat display technology, and more particularly, to a pixel circuit relating to an organic light emitting diode and a display using the same and a driving method thereof.
2. Description of Related Art
Since the years, the developments of the flat display technology are ceaselessly upgraded, wherein organic light emitting diodes (OLEDs), also named as organic electroluminescence (OEL), are used in the flat display technology and play an unique role uncompetitive by other technique as a new age technology and have many advantages including power-saving, ultra slim, light, self-luminescent, no limitation of angle of view (AOV), fast response, high photoelectric efficiency, without backlight structure and color filter structure, high contrast, high luminosity efficiency, high luminance, feasibility of realizing multi-color and RGB devices and wide operation temperature range. Therefore, OLEDs are seen as one of the most perspective flat display technologies.
The OLED display now can be roughly divided into a passive matrix OLED display (PMOLED display) and an active matrix OLED display (AMOLED display). The PMOLED display is driven mainly by using scan means/mechanism so as to produce high luminance. Consequently, the PMOLED display consumes higher power, the devices are easier to be degraded and the display is not suitable for high-resolution panel. The AMOLED display is driven mainly by using thin film transistors (TFTs) to associate with capacitors for storing different data signals, so as to control the grayscale of each pixel on the panel.
With an AMOLED display, after scanning, the pixels still keep the original luminance, and the AMOLED display does not need to drive for a very high luminance. In comparison with the PMOLED display, the AMOLED display has obvious advantages: better lifetime performance and high resolution. As a result, the current development is focused on the AMOLED display towards application in large-sized panel.
As shown by FIG. 1, the pixel circuit 100 of a traditional AMOLED display mostly adopts a 2T1C architecture, i.e., two TFTs T1 and T2 plus a capacitor C. In general speaking, the pixel circuit 100 is driven by a scan signal Vscan and a data signal Vdata to emit light, where the presented luminance thereof is proportional or inversely proportional to the intensity of the data signal Vdata.
In practical, since the high system voltage OVDD of each pixel circuit 100 in an AMOLED display is connected to each other, such that when each pixel circuit 100 is driven by the corresponding scan signal Vscan and data signal Vdata, the current flowing through the wire for transmitting the high system voltage OVDD would produce a voltage-dropping effect in association with the impedance the wire itself has. As a result, the high system voltage OVDD received by each pixel circuit 100 is different from each other.
In addition, under the influence of the process, the TFT T2 for driving the OLED OD in each pixel circuit 100 may have different threshold voltage Vth. Accordingly, based on the high system voltage OVDD received by each pixel circuit 100 is different and the threshold voltage Vth of the TFT T2 for driving the OLED OD in each pixel circuit 100 is not the same, such situations lead to that the currents flowing through the OLEDs OD of the pixel circuits 100 are different from each other even through assuming a same data signal Vdata is applied on each of the pixel circuits 100. Therefore, the luminance presented by each pixel circuit 100 is different, which is considered as the major factor of non-uniform displaying on the OLED panel.